The present invention relates generally to a so-called Bluetooth communications system operating at radio frequencies around 2.45 GHz and, more particularly, to the allocation of an adaptive transmission channel in a piconet operating in the Bluetooth radio frequency band.
A Bluetooth system provides a communication channel between two electronic devices via a short-range radio link. In particular, the Bluetooth system operates in the radio frequency range around 2.4 GHz in the unlicensed Industrial-Scientific-Medical (ISM) band. The Bluetooth radio link is intended to be a cable replacement between portable and/or fixed electronic devices. The portable devices include mobile phones, communicators, audio headsets, laptop computers, other GEOS-base or palm OS-based devices and devices with different operating systems.
The Bluetooth operating frequency is globally available, but the permissible bandwidth of the Bluetooth band and the available RF channels may be different from one country to another. Globally, the Bluetooth operating frequency falls within the 2400 MHz to 2497 MHz range. In the U.S. and in Europe, a band of 83.7 MHz bandwidth is available and the band is divided into 79 RF channels spaced 1 MHz apart. Bluetooth network arrangements can be either point-to-point or point-to-multipoint to provide connection links among a plurality of electronic devices. Two to eight devices can be operatively connected into a piconet, wherein, at a given period, one of the devices serves as the master while the others are the slaves. Several piconets may form a larger communications network known as a scatternet, with each piconet maintaining its independence. The baseband protocol for a Bluetooth system combines circuit and packet switching. Circuit switching can be either asynchronous or synchronous. Up to three synchronous data (logical) channels, or one synchronous and one asynchronous data channel, can be supported on one physical channel. Each synchronous channel can support a 64 Kb/s transfer rate while an asynchronous channel can transmit up to 721 Kb/s in one direction and 57.6 Kb/s in the opposite direction. If the link is symmetric, the transfer rate in the asynchronous channel can support 432.6 Kb/s. A typical Bluetooth system consists of a radio link, a link control unit and a support unit for link management and host terminal interface functions. The Bluetooth link controller carries out the baseband protocols and other low-level routines. Link layer messages for link set-up and control are defined in the Link Manager Protocol (LMP). In order to overcome the problems of radio noise interference and signal fading, frequency hopping is currently used to make the connections robust.
Currently, each of the 79 RF channels is utilized by a pseudo-random hopping sequence through the Bluetooth bandwidth. The hopping sequence is unique for each piconet and is determined by the Bluetooth device address of the master whose clock is used to determine the phase of the hopping sequence. The channel is divided into time slots of 625 xcexcs in length and numbered according to the master clock, wherein each time slot corresponds to an RF hop frequency and wherein each consecutive hop corresponds to a different RF hop frequency. The nominal hop rate is 1600 hops/s. All Bluetooth devices participating in the piconet are time and hop synchronized to the channel. The slot numbering ranges from 0 to 227xe2x88x921 and is cyclic with a cycle length of 227. In the time slots, master and slave devices can transmit packets. Packets transmitted by the master or the slave device may extend up to five time slots. The RF hop frequency remains fixed for the duration of packet transmission.
The ISM frequency bands can be used by many different devices which include wireless local area networks (WLANs), microwave ovens, and lighting equipment. The interference caused by these multiple different applications is inherent to almost any device which is connected to the piconet. Currently, the usage of ISM frequency bands is growing very fast. In order to survive in these frequency bands, new wireless communication systems must utilize a robust modulation scheme with a certain method of channel allocation. For example, WLAN systems are using a Frequency Hopping Spread Spectrum (FHSS) method, in which transmission takes place only a short time in each channel, and Direct Sequence Spread Spectrum (DSSS) modulation, which overcomes narrow-band interference by spreading. However, in these systems the allocation of channels, or channelization, is organized by using either a carrier sensing (CS) method or a Code Division Multiple Access (CDMA) method. In the CS method, each of the channels which are to be used is measured in order to determine whether a transmission is taking place in that channel. If the channel under measurement does not have an ongoing transmission, then the channel can be used for hopping. The major problem with the carrier sensing method is that the measurement is ineffective for the traffic type that uses a different modulation method. In the CDMA method, while the narrow-band interferer is spread in the receiver, the received noise is actually increased, thereby reducing the noise margin of the system. Optionally, it is also possible to establish virtual traffic channels by using different hopping frequencies. However, this does not avoid the parts of the spectrum where the interference occurs.
It is advantageous and desirable to provide a method and system for making connections between devices operating in the ISM bands by effectively avoiding the parts of the spectrum where channel conditions such as interference and noise levels may adversely affect the channel connection.
The primary objective of the present invention is to provide a method and system to ensure the backward compatibility of a piconet device which is capable of operating in the non-frequency-hopping fashion (BT 2.0) in an environment where the frequency-hopping fashion (BT 1.0) is also used. The backward compatibility ensures that a BT 2.0 device is compatible with a BT 1.0 device.
Accordingly, the present invention provides a method for establishing a connection link between a master device and a plurality of slave devices in a communications network having a plurality of frequency channels within a radio frequency band, wherein the connection links between the master device and the slave devices are capable of being carried out in a frequency-hopping fashion. The method comprises the steps of:
sending a link request to the master device requesting establishment of a non-frequency-hopping connection link between the master device and a slave device;
establishing the non-frequency-hopping connection link as requested if the master device is able to select a communication channel for said non-frequency-hopping connection link; and
establishing or maintaining the connection link in the frequency-hopping fashion if the master device is unable to select the communication channel for said non-frequency-hopping connection link.
Preferably, the method further comprises the step of measuring channel conditions including the carrier power of the channel and the interference and noise levels affecting the connection link in order for the master device to select the communication channel for the non-frequency-hopping connection link. The measurement of channel conditions is carried out by the master device or the requesting slave device.
Preferably, the method also includes the step of sending to the requesting slave devices a plurality of measurement parameters including measurement time and frequencies to be measured in order for the slave device to measure the channel conditions based on the measurement parameters.
Preferably, the method also includes the step of sending a measurement report to the master device by the slave device reporting results of the channel condition measurements.
Upon establishing the non-frequency-hopping connection link with the slave device, the master device can give up or retain its role as a master device to the non-requesting slave devices.
The present invention also provides a system for the adaptive allocation of transmission channels in order to establishing a connection link between a master device and at least one slave device in a communications network having a plurality of frequency channels within a radio frequency band, wherein the connection link between the master device and the slave device is capable of being carried out in a frequency-hopping fashion. The system comprises:
a mechanism for the slave device to request the master device to allocate a channel for a connection link in a non-frequency hopping fashion;
a mechanism for the master to determine whether it is able to allocate the requested channel;
a mechanism to establish the non-frequency-hopping connection link between the master device and the requesting slave device on the allocated channel if the master is able to allocate the requested channel; and
a mechanism to establish or maintain a frequency-hopping connection link between the master device and the requesting slave device if the master is unable to allocate the requested channel.
Preferably, the slave device maintains the frequency-hopping connection link if the slave device fails to receive a response from the master device responding to the request.
The present invention will become apparent taken in conjunction with FIGS. 1a to 15.